As a common method of measuring blood glucose levels, an oxidation-reduction reaction is used. On the other hand, for handy measurement of the blood glucose levels at home and elsewhere, palm-size, portable blood glucose measuring devices are used widely. These handy-type blood glucose measuring devices make use of a disposable-biosensor which also serves as an enzyme reaction field. The blood glucose level measurement is made by supplying the blood to the biosensor.
Sensitivity of the individual biosensors can vary from one biosensor to another. The variation can be a result of difference in row materials, design changes in production lines and so on. Especially, when starting up the production line, due to needs for optimizing various conditions in the production line and selecting suitable materials, sensitivity variations among the produced sensors tend to be large. Further, when there are plural manufacturing plants or plural production lines of the biosensors, sensitivity variation among the plants or production lines can result. In preparation for these sensitivity variations, some blood glucose measuring devices incorporate a plurality of calibration curves. In addition, if the tester is capable of not only measuring the blood glucose level but also other values such as cholesterol level, a plurality of calibration curves must be prepared so that each kind of the components can be measured. In these cases, arrangements must be made so that the measuring device can recognize the sensitivity of each biosensor as well as information necessary for relating the calibration curve with the target component so that appropriate one of the calibration curves will be selected for a given measurement.
A first example for such selection of the calibration curve is that each of the plural calibration curves is given an identification code. The biosensor ID code will then be printed on boxes or instruction sheets of the biosensors. In this arrangement, the blood glucose measuring device incorporates a calibration curve selection program for example, which selects an appropriate calibration curve when the user makes an input to the blood glucose measuring device using buttons.
A second example for the selection of the calibration curve is that each box of the biosensors will include an adjustment chip which can supply calibration curve information on the biosensors packed in the box. In this case, the user inserts the adjustment chip into the blood glucose measuring device just the same way as he uses the biosensor. Then, the blood glucose measuring device will automatically select an appropriate calibration curve.
A third example for the selection of the calibration curve is disclosed in the Japanese Patent Laid-Open No. 10-332626. According to the invention disclosed in the gazette, the biosensor is provided with production-lot identifying electrodes separately from concentration level measuring electrodes, and the biosensor outputs signals corresponding to the locations of the production-lot identifying electrodes. The blood glucose measuring device on the other hand has a plurality of determining terminals corresponding to the production-lot identifying electrodes. The blood glucose measuring device uses these determining terminals to pick up the signals corresponding to the locations of the production-lot identifying electrodes, so that the blood glucose measuring device can choose an appropriate calibration curve based on the signals obtained from the biosensor.
However, if the calibration curve selection is relied upon the button operation or the chip insertion to be performed by the user, the user has to do the additional burden of selecting the calibration curve, and even worse is a possibility that the user forgets the operation to select an appropriate curve. If the user forgets the selection of the calibration curve, it becomes impossible to perform blood glucose level measurement truly adjusted for the sensitivity variation of the sensor, etc. Therefore, it is not a good option to depend upon the user in the selection of calibration curve.
Use of the adjustment chip requires a production line for the chips separately from those for the biosensors, which would lead to disadvantages in terms of manufacturing cost.
Use of the production-lot identifying electrodes poses a challenge that the sensitivity of the biosensor must be forecasted and the calibration curve information must be inputted into the biosensor at an early stage of the production. If a large discrepancy is found between the actual sensor sensitivity and the forecast sensitivity, the produced biosensors cannot be distributed through the market, resulting in decreased yield. Thus, there is potential disadvantage in terms of the manufacturing cost.